The present embodiments relate to a method for determining the range (path length or depth) of radiation, and to an apparatus that determines the range of radiation.
“Relation between carbon ion ranges and x-ray CT numbers” (O. Jäkel, C. Jacob, D. Schardt, C. P. Karger, G. H. Hartmann; Medical Physics, Vol. 28, No. 4, April 2001, pp. 701-703) addresses the range of particle radiation in various phantom materials and in bone. Various types of tissue, including muscles, fat and lungs, were simulated with phantom materials. Range measurements were performed with the aid of an absorber. The absorber contains water in a variable layer thickness. The absorber, in addition to the phantom material, was positioned between two ionization chambers. The irradiation was perpendicular to the ionization chambers used for the charge measurement. A relationship was ascertained in various materials between the attenuation of X-radiation, which can be determined by computer tomography, and the range of particles, such as carbon ions and protons.
German Patent Disclosure DE 10 2004 057 726 A1 discloses a medical examination and treatment system. The examination and treatment system includes a radiation source that emits particle radiation, such as ion radiation. The examination and treatment system has both an X-ray emitter, disposed on the side of the target volume opposite the radiation source, and a detector. The purpose is to enable both time-saving scanning and precise radiation therapy. The irradiation profile of the particle beam may be monitored. However, determining the range of the particle radiation is not the subject of DE 10 2004 057 726 A1.
In particle-beam therapy, it is important that the range of the radiation used in the target volume be predicted as precisely as possible. Unlike electromagnetic radiation, particle radiation has an inverted dosage profile. The radiation dose deposited in the target volume exposed to the radiation increases with increasing penetration depth, and it reaches a sharp maximum point just before the maximum range. The inverted dosage profile spares the tissue located in the beam path ahead of the target volume to be treated. Optimal radiation planning demands that the location of the maximum point of the dosage profile be known precisely.